This invention relates to diene polymerization, particularly to high-cis diene polymerization. More particularly, the present invention relates to a high-cis, low gel polydiene and a process for producing the same.
High cis polydienes have been prepared using an organonickel based catalyst system. The use of the organonickel based catalyst system can result in a rapid rate of polymerization, and the ability to control various polymer properties by varying the catalyst ratios. Moreover, organonickel based catalyst systems are generally hardy catalysts that may be able to maintain catalytic activity at a wide range of polymerization conditions. The use of organonickel catalysts to form high cis polydienes relies on the need for a fluorine-containing co-catalyst, such as HF or BF3. These co-catalysts, however, may be cumbersome to work with as they tend to generate strong acids when contacting water, leading to possible equipment corrosion and possible gel-formation of the polymer. Moreover, the reaction products of the co-catalysts include trialkylboranes when BF3 is used, which can react with molecular oxygen to form peroxyboranes, compounds that may spontaneously homolytically break to form radicals, increasing the gel content upon aging of the finished products.
A variety of terminators, including water, alcohols, polyols, amines, and carboxylic acids have been used to terminate nickel-catalyzed diene polymerizations. Although such terminators may be effective in the termination of the diene polymerization, the protic solvents are capable of reacting with fluoride containing compounds in the polymerization mixture, generating strong acids, which may lead to corrosion problems in the finishing equipment and can also lead to cationic coupling (gelation) of the finished polymer.
Amine termination is another method that has been used in previous syntheses of high-cis polydienes, with the amine acting as a base to neutralize. any acidic compounds in the polymerization mixture, reducing corrosion and cationic gellation. The bases thus formed also react with trialkylboranes to form Lewis acid-Lewis base complexes. These complexes reduce the reactivity of trialkylboranes toward oxygen, thus reducing the generation of radicals, which leads to gel formation. Unfortunately, such amine terminators are often quite, expensive, thus increasing the cost of the overall process.
It would thus be desirable to develop a system for terminating the synthesis of high-cis polydienes that would be capable of overcoming the increased gel content and/or equipment corrosion experienced with the above, mentioned termination systems while maintaining or reducing costs.
The present invention is directed to a process for forming a high-cis polydiene. The process includes catalyzing a diene polymerization, and terminating the polymerization with a termination mixture comprising an inorganic base and at least one of an amine and a carboxylic acid.
In another embodiment, the present invention is directed to a polymer composition including a high-cis polydiene terminated with an inorganic base and at least one of an amine and a carboxylic acid. The polydiene preferably has a cis content greater than about 85-90% and a static gel content less than about 5%.
In a third embodiment, the present invention is directed to a process for producing high-cis polydienes. The process includes a continuous polymerization of a nickel catalyzed polydiene terminated by a termination mixture comprising sodium hydroxide and at least one of an amine and a carboxylic acid.